You can't (well, shouldn't) try and run some speakers off the factory amp, and others off an aftermarket amp. The factory amp for the Alpine and HK system has the crossovers built into it, so certain frequencies go to the dash, doors, sub, etc, and you can't change any of that. So if you try and run a separate amp to part of the system, you can only tune that part of it, not the factory powered part, and you can't ever tune it correctly. You're best off to a) add a sub/subs + mono amp to power them and bypass the factory sub. Swap out the factory speakers, but don't try to amplify them. Or b) bypass the factory amp entirely, get a DSP + amplifier (or combo) for everything + subs. If you go with option b, you can get as crazy as your budget allows. DSP brands vary greatly - I'd do a lot of research before picking one. Check out reviews, features, etc. Try to download the software and play with it if you plan to learn how to use it yourself (vs having your installer do it all for you). Some brands are: Audio Control, JL, Focal, ARC, Helix, Mosconi